The special representative for North Korea policy in the State Department will be in Seoul until Thursday for talks with senior security officials including his counterpart Kim Hong-kyun.

Yun came to Seoul late Monday from Beijing where he met with Chinese officials to coordinate responses to the North's growing nuclear and missile threats.

He met with two centrist presidential hopefuls -- South Chungcheong Province Gov. An Hee-jung and former ruling party floor leader Yoo Seung-min -- and their key diplomatic and security advisers, the sources said.

An, affiliated with the liberal Democratic Party, ranked second in a poll conducted last week, with 15.6 percent approval rating.

Yoo from the conservative Bareun Party took the seventh place with 3.8 percent.

A source denied media speculations that Yun would meet other candidates, including Moon Jae-in, the former leader of the Democratic Party and Ahn Cheol-soo, a former co-chair of the People's Party. The source, however, did not rule out the possibility of meetings with their campaign officials. Moon remains a frontrunner with 36.6 percent support, while Ahn sits in third place with 12 percent. 

An adviser to Gov. An told Yonhap News Agency that the meeting between An and Yun was arranged at the request of the US side.

"The two sides discussed a wide range of diplomatic and security issues, including THAAD, North Korea and China policy," he said on condition of anonymity. "The meeting lasted more than one hour. It was productive and in a good mood."

He declined to elaborate, saying they promised not to disclose details to the media.

South Korea will hold an early presidential election on May 9 following the Constitutional Court's ruling to oust Park Geun-hye as president on March 10 over a massive corruption scandal.

Observers say that Yun met with the politicians to reaffirm their commitment to the Korea-US alliance and continued policy coordination amid augmenting geopolitical uncertainties including an escalating threat from the North and a sudden election in the South. (Yonhap)